I would use one of the currency brokers. Try
www.hifx.com. You can pick the exchange rate you want to change at, do it in advance by paying a deposit up front and its all done at no cost to you. They do not charge commssion, they make their money by keeping the excess. (ie if you picked $2.50 and it went up to $2.51 they would cream off the 1 cent). They deal in millions so they make enough money to get by.
No I do not work for them, they were recommended to me same as I am doing to you.